An intraocular lens is inserted, for vision correction, into an eyeball after removing the crystalline lens due to cataract or the like. A spherical design is the mainstream of the current optical designs for an intraocular lens, because the design has many functions required for an intraocular lens moderately, is easy to manufacture, and is convenient for managing powers. However, an intraocular lens is also being developed with attention being paid to a specific function and with an aim for enhancing the function. The technological trends for enhancement of such specific function can be classified into two types. The first trend is directed to enable an eye to see both near objects and distance objects. The second trend is directed to enable an eye to see an object more clearly.
A typical intraocular lens of the first trend as described above is a multifocal intraocular lens, in which the optical region of the intraocular lens is divided into a plurality of zones, with each zone having a power distribution for seeing near objects, a power distribution for seeing intermediate objects, and a power distribution for seeing distance objects, respectively. The optical designs thereof differ depending on which distance priority is given to. In any of the designs, however, the quantity of light which enters each zone is smaller compared with a case of a spherical lens which captures light with the entire lens. As a result, despite an increased visible range, contrast of such lens is deteriorated (for example, see Patent Document 1).
An invention described in Patent Document 2 is based on a similar technological concept. Although the invention does not cover all of near, intermediate, and distance, it is directed to provide a wider visible range compared with a spherical lens, for example, with an enhanced depth of focus for near vision. Needless to say, an intraocular lens according to the invention results in a deteriorated contrast compared with a spherical lens.
On the other hand, a technology of the second trend is based on the concept which is dramatically opposite to the concept of the first trend. That is, the technology is directed to improve contrast, while sacrificing the size of the visible range. When a spherical intraocular lens is inserted into an eye, focal points are not concentrated on the retina because the aberration of the cornea itself and the aberration of the intraocular lens are overlapped with each other. The second trend is directed to reduce the aberration. The spherical aberrations of the cornea and of the intraocular lens increase, with increasing radial distance from the optical axis. That is, although influence due to the spherical aberration is little if a width of a light ray entering the eye is small, it is significant if the width of the light ray is large. For example, a driver has a pupil diameter equal to or greater than 3.2 mm when s/he drives a car at night. Such pupil diameter is greatly affected by the spherical aberration such that the contrast of an object is deteriorated, which may be dangerous for driving a car. A technology of the second trend is directed to solve this kind of problem (for example, see Patent Documents 3, 4 and 5).
All technologies disclosed in Patent Documents 3 to 5 are directed to reduce the spherical aberration. However, they have an disadvantage that they provide a smaller visible range compared with the spherical lens due to smaller depth of focus. These aberration correction lenses are directed to reduce the spherical aberration which would otherwise increase with increasing radial distance from the optical axis. Accordingly, these lenses have simpler power distributions compared with a multifocal lens.    [Patent Document 1] Japanese Patent Application Laid Open No. S60-85744    [Patent Document 2] Published Japanese Translation of a PCT Application No. 2000-511439    [Patent Document 3] U.S. Pat. No. 4,504,982    [Patent Document 4] Published Japanese Translation of a PCT Application No. 2003-534565    [Patent Document 5] Japanese Patent Application Laid Open No. 2006-14818